This invention relates, generally, to polishing slurries and their use in polishing systems and, more particularly, to methods for polishing work pieces using a reconstituted dry particulate polishing composition.
Polishing formulations for the chemical-mechanical-polishing (CMP) of integrated circuit wafers, as well as polishing compounds for high technology optical components or other ultra fine surface finish applications, typically consist of an aqueous dispersion of solids (the abrasives) combined with a variety of chemical constituents. Such commercial materials can be sold as a single mixture of solids or in several parts, one part containing the abrasive component in a concentrated form, and the other part containing the chemical component(s) in a concentrated form.
As the technology of CMP polishing has become more critical, complex chemical and abrasive systems have been developed. These aqueous formulations must exhibit long shelf life and good stability so that the materials do not change while in storage. Uncontrolled or excessive physical changes during storage can render these formulations unusable for their intended purpose. For example, when a mixture of solids is stored and the solids settle in the storage container to form a hard, sediment, the mixture is no longer readily usable by the customer. Also, if the chemical system undergoes significant changes in the concentrations of the reactive species, the slurry can be rendered unusable for its intended purpose.
Frequently the main reason for physical and chemical instability is that slurries are typically packaged for sale as aqueous dispersions. More recently, CMP polishing systems have been developed in which the abrasives are contained in a polishing pad and are not contained in the liquid polishing composition provided at the polishing interface. However, the liquid polishing compositions used with these types of polishing pads often exhibit to the same types of chemical instability observed in the conventional aqueous dispersion slurries.
Preparing a solid particulate slurry composition and drying the composition can address the instability of a liquid-dispersion polishing slurry. The stability issues for both the chemical and abrasive constituents can be minimized by eliminating the xe2x80x9caqueousxe2x80x9d part of the system. Accordingly, a dry, particulate slurry is prepared having a composition exactly as the final end user would use it. By preparing a such a dry slurry composition, the slurry is effectively xe2x80x9cfrozen in timexe2x80x9d so that it will be exactly as the end user wants it, up to six months or longer after the dry slurry composition is originally prepared. Such a slurry composition is disclosed in co-pending, commonly-assigned patent application filed Oct. 6, 1999 and having Ser. No. 09/413,083. In accordance with the disclosed method, the dry particulate slurry composition is simply reconstituted prior to use. While the development of dry slurry preparation methods has greatly improved the ability to store slurry compositions over extended periods of time, further development of methods of using reconstituted slurries can provide even more improved polishing methods.
The present invention provides a polishing method using a dry particulate solids composition comprised of a chemical-mechanical polishing composition comprising chemicals useful for CMP that has had substantially all water removed therefrom and the can be reconstituted into a chemical-mechanical polishing composition ready for use. This composition is delivered via one of a variety of methods to an apparatus for reconstitution into an aqueous polishing solution. The dry particulate solids composition may comprise abrasive particles, an oxidizing agent, a complexing agent, a surface passivating agent, a surfactant, a dispersant, or any other type of compound used in slurries for chemical-mechanical polishing.
The quantity of dry particulate solids delivered to the reconstitution apparatus can be an amount appropriate for polishing one work piece or a small number of work pieces, or the system can operate in larger batches or a continuous flow mode. The reconstituted aqueous polishing solution may then be monitored for physical or chemical properties, filtered, blended with other chemical mixtures, or modified in other ways prior to being used in a polishing operation.
In one embodiment, the inventive process includes providing a dry particulate solids composition and reconstituting an amount of the dry particulate solids composition to form a quantity of an aqueous composition. The amount of the aqueous composition is just substantially sufficient to complete the polishing of the predetermined number of work pieces.
In another embodiment, the process of the invention includes determining a fixed number of work pieces to be polished and preparing a quantity of the dry particulate solids composition that is just sufficient to form an amount of reconstituted slurry for completing the polishing the fixed number of work pieces.